Method of producing a photographic film base having a subbing layer

ABSTRACT

Coating of biaxially oriented polyester films with a subbing composition including a polymeric and a water-permeable component such as gelatin before the film is fully oriented.

United States Patent [1 1 Nerurkar et al.

[ METHOD OF PRODUCING A PHOTOGRAPHIC FILM BASE HAVING A SUBBING LAYER[75] Inventors: Mohanial Shantaram Nerurkar; Paul Ernest Dawson, both ofWelwyn Garden City, England [73] Assignee: lmperial Chemical IndustriesLimited, London, England [22] Filed: Feb. 1, 1971 [21] App1.No.: 111,749

[30] Foreign Application Priority Data Feb. 6, 1970 Great Britain'5,794/70 [52] US. Cl 117/7, 117/34, 117/47 A,

[56] References Cited UNITED STATES PATENTS 3,212,897 10/1965 Secrist..117/34 [451 Aug. 7, 1973 3,320,191 5/1967 Secrist 117/34 3,501,3033/1970 Foltz 96/88 3,271,178 9/1966 Nadeau et a1..... 117/7 3,600,2088/1971 Abbott et a1 117/7 2,779,684 1/1957 Alles 1 117/34 2,627,0882/1953 Alles et a1 117/34 3,590,107 6/1971 Smith et a1 117/47 A3,576,658 4/1971 Notomi et a1 117/7 3,082,144 3/1963 Haley 117/343,508,944 4/1970 Henderson eta1.... .1 117/7 3,285,766 11/1966 Barkis eta1 I 17/7 3,535,147 10/1970 White 117/7 FORElGN PATENTS OR APPLICATIONS925,069 5/1963 Great Britain 986,923 3/1965 Great Britain PrimaryExaminerWi1liam D. Martin Assistant Examiner-Wil1iam R. TrenorAtt0rney-Cushman, Darby & Cushman [57] ABSTRACT 9 Claims, No DrawingsMETHOD OF PRODUCING A PHOTOGRAPHIC FILM BASE HAVING A SUBBING LAYER Thepresent invention relates to a method of coating a synthetic polymericfilm for the production of a photographic film base and to thephotographic film base produced.

It is known that photographic film bases may be produced fromdimensionally stable filmsformed from hydrophobic synthetic polymericmaterials, such as polyesters, e.g. polyethylene terephthalate, andpolycarbonates. A light sensitive layer, formed for example from agelatino silver halide emulsion, may be applied to the photographic filmbase. However, since the polymeric film is hydrophobic and the lightsensitive layer is hydrophilic it is difficult to develop sufficientadhesion between the polymeric film and the light sensitive layer whichwill be maintained not only during the normal handling of the sensitivefilm but also through the wet processing operations to which it issubjected.

For this reason it has been common practice to coat the surface of thesynthetic polymeric film, such as a polyethylene terephthalate film,after biaxial orientation and heat-setting, with one or more anchoringlayers, often termed subbing" layers, which adhere to the syntheticpolymeric film and to which the light sensitive layer will adhere. Forexample, such polymeric films have been coated with a polymeric subbingcomposition which contains a copolymer or terpolymer of vinylidenechloride with, for example, an alkyl acrylate and an unsaturated organicacid. A gelatin subbing composition is generally applied over thepolymeric subbing coating. The light sensitive layer has then beenapplied over the polymeric subbing coating, or ifa gelatin subbingcoating is also used, over that.

It has also been common practice to imporve the adhesion between thefilm base and the subbing coating applied to it by first treating thefilm surface with an oxidising agent such as an aqueous solution ofpotassium permanganate or solvent etching with e.g. ochlorophenol. I

As an alternative to applying the polymeric subbing coating afterorientation and heat setting of the polymeric film, such a coating hasbeen applied prior to or in between the two stretching operationsemployed to orient the film. However, it has not been common practice toapply a gelatin subbing coating prior to or in between the drawingoperations.

ln accordance with the present invention a method of producing aphotographic film base comprises casting a flat polymeric film,molecularly orienting the cast film by stretching it in at least onedirection and coating the film with a subbing composition comprising apolymeric component and a water permeable component prior to thecompletion of the molecular orientation.

The photographic film base produced according to the invention comprisesa flat polymeric film, which has been molecularly oriented in at leastone direction and coated with a subbing composition comprising apolymeric component and a water permeable component.

The polymeric film may be formed from anyhydrophobic synthetic polymericmaterial, and should produce a dimensionally stable film afterorientation and heat setting. Suitable polymeric materialsincludepolyesters, e.g. polyethylene terephthalate, copolyesters andpolycarbonates. Our preferred polymeric material is polyethyleneterephthalate.

In order that the photographic image produced on the film base accordingto this invention should not become distorted, the polymeric film shouldbe dimensionally stable under the normal conditions of use andphotographic processing, e.g. development and fixing. Whilst it isenvisaged that some uniaxially oriented polymeric films may besufficiently dimensionally stable, it is normally necessary to biaxiallyorient the polymeric films to obtain the desired dimensional stability.When polyethylene terephthalate film is employed it is generallybiaxially oriented.

Generally, biaxially oriented polymeric films may be oriented firstly bystretching in the longitudinal direction followed by stretching in thetransverse direction. The biaxially oriented film may then be heat setby heating whilst restraining the film against shrinkage in thelongitudinal and transverse directions. A further stretching in thelongitudinal direction may be employed before or after heat setting toimprove the tensile strength in the longitudinal direction.

An alternative method of improving the longitudinal tensile strength isto stretch firstly in the transverse direction and subsequently in thelongitudinal direction.

A further method of biaxially orienting the film is to stretch itsimultaneously in the longitudinal and transverse directions.

All of the above methods of biaxially orienting the polymeric film areknown and may be employed in carrying out the present invention.Orientation is effected by stretching at a temperature below thesoftening temperature of the film but above its second order transitiontemperature.

A typical process which may be employed in the present invention forbiaxially orienting polyethylene terephthalate film which has been caston to a drum on which it has been quenched to below C involvesstretching the film at a temperature in the range 80 to C in thelongitudinal direction between two sets of fast and slow nip or capstanrollers which apply a draw ratio of 2.5:1 to 4.0:1 and stretching thefilm in the transverse direction at a temperature in the range from 80to C and above the temperature employed for stretching in'thelongitudinal direction. The stretching in -the transverse direction maybe effected in a'stenter apparatus at a draw ratio of 2.5:1 to 4.0:1.The film is then heat set by heating at a temperature in the range to250C for 0.5 to 5 minutes while being restrained from shrinkage in bothdirections, conveniently by holding the film with a stenter apparatus.The heat set film may then optionally be drawn in the longitudinaldirection to improve its longitudinal tensile strength, at a temperatureinthe range l00'to 220 using a draw ratio of 1.5:1 to 3.011.

'If the film is produced by a process in which it is stretched firstlyin the transverse direction and then in the longitudinal direction so asto improve its longitudinal tensile strength it maybe stretched at drawratios of at least 3. 3:l in the'transverse direction and from 3.0:1to"6.0:l in the longitudinal direction.

According to the present invention, the subbing composition is appliedprior to the completion of the molecular orientation, that is thestretching operation or operations employed to orient the film. ltmaybeapplied before any orientation is effected, e.g. in the case of abiaxially oriented polyethylene terephthalate film,

after the polymeric film has been cast on to the quenching drum andbefore the first stretching operation which will be in either thelongitudinal or transverse direction, normally the former.Alternatively, for a biaxially oriented film which is made by stretchingin sequence in two substantially mutually perpendicular directions thesubbing composition may be applied between the stretching operationemployed in each direction. Accordingly, if the film is stretched in thelongitudinal direction first, then the subbing composition may beapplied after stretching in the longitudinal direction but beforestretching in the transverse direction. Conversely, if the film isstretched in the transverse direction first, then the subbingcomposition may be applied after stretching in the transverse directionbut before stretching in the longitudinal direction. When a secondstretching operation is effected in the longitudinal direction toimprove the longitudinal tensile strength of the film the subbingcomposition may be applied before that stretching operation.

The techniques and apparatus adopted for applying the subbingcomposition to the film may consist of any techniques and apparatusknown in the art.

It has been found that when a subbing composition is applied to thepolymeric film in accordance with the present invention it is notnecessary to pre-treat the surface of the film prior to subbing as hasoften been done in the past with, for example, an oxidising agent or asolvent etching agent. However, if desired, components of this naturemay be included in the subbing composition as described below.

The polymeric component of the subbing composition may consist of anysuitable synthetic polymer copolymer or terpolymer which provides anadequate adhesion to the polymeric film. One or more polymers orcopolymers may be employed to form a composite polymeric component ifdesired.

A preferred group of copolymers suitable for forming the polymericcomponent of the subbing composition comprises copolymers of conjugateddiolefines with one or more vinyl comonomers. The conjugated diolefinemay for example be butadiene or isoprene and the vinyl comonomer orcomonomers may be chosen from acrylonitrile, styrene, methylmethacrylate, methacrylic acid and itaconic acid. Terpolymers in whichone of the vinyl comonomers is an unsaturated carboxylic acid,preferably itaconic acid, are particularly useful, for instanceterpolymers of butadiene, styrene and itaconic acid as specified belowhave been found to be satisfactory. ltaconic acid is a usefulconstituent as it promotes adhesion to gelatin and therefore assists indeveloping a bond to a gelatin-containing layer which may be appliedover the subbing layer.

The relative proportions of conjugated diolefine and vinyl comonomer orcomonomers in the copolymer are chosen to provide a subbing compositionwhich will not be impaired by the stretching operations used for theorientation of the film to which it is applied. Generally to 50 molepercent, preferably 25 to 40 mole percent, of the conjugated diolefineis used. The proportion employed in practice depends upon the nature ofthe conjugated diolefine and the vinyl comonomer or comonomers. If toolittle conjugated diolefine is used the copolymer tends to be brittleand becomes hazy when the film to which it is applied is stretched. Iftoo much conjugated diolefine is used the copolymer tends to be soft andthe subbed film tends to block when it is reeled. When a terpolymercontaining an unsaturated carboxylic acid such as methacrylic acid oritaconic acid is used the proportion of acid should not exceed 20 molepercent, the relative amounts of the terpolymer constitutents being suchthat the subbing composition is resistant to stretch haze and blocking.It has been found that terpolymers comprising 25 to 40 mole percentbutadiene, 53 to 74.5 mole percent styrene and 0.5 to 7 mole percentitaconic acid are suitable polymeric components for the subbingcompositions of the invention.

Alternatively, polymers, copolymers and terpolymers of a vinylhalogenoester or a vinyl cyanoester may be used as the polymericcomponent. Suitable materials are those disclosed in BritishSpecifications 1,208,821

and 1,208,822. Preferably, copolymers or terpolymers of vinyl mono, dior tri-chloroacetate or vinyl mono, di or tri-bromoacetate are usedwhich contain units derived from n-butyl acrylate; 2-ethoxyethylacrylate; ethyl acrylate; 2-ethylhexyl acrylate; decyl methacrylate;octa decyl methacrylate; 2-ethylhexyl methacrylate;di-(polypropyleneoxy) itaconate; vinyl butyl ether; vinyl ethyl ether;vinyl methyl ether; vinyl isobutyl ether; vinyl stearate; vinylversatate; vinyl pivalate; ethylene; butadiene; 4-dodecyl styrene; or4-nonyl styrene; optionally together with units derived from itaconicacid; maleic acid; citraconic acid; acrylic acid; methacrylic acid;crotonic acid; di-esters and mono esters of unsaturated di-carboxylicacids with monohydric or polyhydric alcohols; allyl alcohol; vinylalcohol; esters of unsaturated mono-carboxylic acids with polyhydricalcohols, e.g. 2-hydroxyethyl methacrylate; vinyl acetate;acrylonitrile; acrylamide; methacrylamide; N-(l,l-dimethyl-3-oxobutyl)acrylamide; N-mono or N,N-di-substituted derivatives of unsaturatedamides, e.g. tertiary butyl acrylamide, N,N-dimethyl acrylamide,N-methylal acrylamide; N-methoxy methyl acrylamide; N-acetoxy methylacrylamide; N-vinyl pyrrolidone or dimethyl amino-ethyl methacrylate.

Further alternative formulations for the polymeric component includepolyvinylidene chloride or conveniently a copolymer or terpolymer ofvinylidene chloride containing at least 35 mole percent of vinylidenechloride. Copolymers and terpolymers of vinylidene chloride may, forinstance, be foremd with vinyl acetate, vinyl propionate; vinylchloroacetate; vinyl chloride; vinyl bromide; methyl, isobutyl orchloroethyl methacrylate; methyl chloroacrylate; itaconic acid and themethyl, ethyl and butyl esters of itaconic acid; acrylonitrile;methacrylonitrile; styrene; and acrylic esters, such as methylmethacrylate, ethyl methacrylate, butyl methacrylate, methyl acrylate,ethyl acrylate, propyl acrylate and butyl acrylate, and acrylic andmethacrylic acids. Suitable terpolymers of vinylidene chloride compriseto mole percent of vinylidene chloride, 4 to 20 mole percent of anacrylic ester such as methyl acrylate and 0.5 to 5 mole percent ofitaconic acid.

The water permeable component of the subbing composition may consist ofany suitable hydrophilic material base, such as gelatin and derivativesof gelatin, which will provide adequate adhesion to another layer, e.g.a light sensitive layer or a further subbing layer applied to the film.

The subbing composition according to the invention may be made up in anorganic or aqueous medium for the polymeric component and the waterpermeable component. If an aqueous medium is used the polymericcomponent is generally present as a dispersion and the water permeablecomponent as a solution. If an organic medium is used the polymericcomponent is generally present as a solution and the water permeablecomponent as a dispersion. The subbing composition may be made up byadding the water permeable component, e.g. gelatin, to the polymericcomponent during the polymerisation of that component, i.e. it may bepart of the polymerisation recipe. The mixture is then mixed with theorganic or aqueous medium. The solution or dispersion may include othercompatible additives which are commonly used in known polymeric subbingcompositions or in known water permeable compositions, e.g. gelatin,subbing compositions. For instance additives which have a swelling orsolvent action on the surface of the film may be included, e.g.chloro-substituted aliphatic acids, such as trichloroacetic acid;phenols and chloro-substituted phenols such as mono-, di-, andtri-chlorophenol; and aromatic alcohols such as resorcinol. Gelatinhardeners such as formalin may also be included. Other useful additiveswhich include dispersing agents, antioxidants, and antiblocking agentsmay be used.

The organic or water medium must be removed by drying and this can beaccomplished in the preheating for the subsequent stretching operation.

Preferably the amount by weight of the water permeable component doesnot exceed the amount of the polymeric component. The ratio of polymericcomponent to the water permeable component in the subbing composition,and indeed in the coating of the oriented and heat set film, isconveniently in the range 2:1 to 40:1 by weight, preferably 3.3:1 to20:1 by weight (i.e. the amount of the water permeable component is 5 to30 percent by weight of the polymeric component).

The subbing composition may conveniently contain 0.05 to 7 percentpreferably 0.4 to 2 percent by weight of the water permeable componentand 2.0 to 15.0 percent, preferably 5.0 to 12.0 percent by weight, ofthe polymeric component, the rest of the composition comprising theorganic solvent or water and any additives employed.

The coat weight of the subbing coating applied to the polymeric film maybe varied by altering the amounts of the polymeric component and thewater permeable component in the subbing composition and/or the rate ofcoating. The applied coat weight on each side of the finished film, i.e.after drying, orientation and heat setting, is preferably in the rangefrom 1 to 7 mg/dm.

It has been found according to one aspect of the invention thatsatisfactory adhesion is produced between the subbing layer and thepolymeric film and also that satisfactory adhesion is produced betweenthe subbing layer and a light sensitive layer such as a gelatino silverhalide emulsion applied directly over it by any means known in the art.The present invention also relates to such photographic films obtainedby applying a light sensitive layer to the film base.

Thus in this instance the present invention now makes it possible toeliminate l) the pretreatment of the polymeric film surface which hasoften beem employed prior to subbing and 2) the multi stage subbingoperations which have often been employed to apply a polymeric subbinglayer and then a gelatin subbing layer, the latter being applied afterthe film has been biaxially oriented and heat set. By the presentinvention a subbing composition can be applied in a single opera- 'tionduring the manufacture of the polymeric film, thereby making it possibleto carry the manufactured film direct to the application of thesensitive emulsion layer without requiring any intermediate subbingoperation.

According to another aspect of the invention a conventional gelatinsubbing composition may be applied over the polymeric/water permeablesubbing layer of the film base after it has been heat set. Excellentadhesion is produced between the two subbing layers. The gelatincomposition may be applied as part of a continuous process whichincludes the production of the polymeric film and its coating with thepolymeric/water permeable subbing layer, the gelatin composition beingapplied after the film has been heat set. Alternatively the gelatincomposition can be applied to the film base made according to theinvention in an independent operation. A light sensitive layer such as agelatino silver halide emulsion may be applied over the gelatin subbinglayer to produce a photographic film. The invention also relates to sucha photographic film.

In order to produce a satisfactory bond between the gelatin subbinglayer and the polymeric subbing layer of a conventional subbed film ithas been common practice to heat or season the film at 100 to 130C for aresidence time of l to 5 minutes. It has now been found that when agelatin subbing layer is applied over the polymeric/water permeablelayer of the film base according to the invention a satisfactory bondbetween the two can be obtained by using seasoning temperatures lowerthan 100C and down to C, preferably around C for the same residencetime, i.e. l to 5 minutes.

Polymeric film is generally susceptible to differential shrinkage acrossits area when heated at an elevated temperature. The extent of thedifferential shrinkage increases with an increase in the temperatureand/or time of the thermal treatment. Accordingly, the use in thepresent invention of seasoning temperatures lower than normal reducesthe differential shrinkage in the film with the result that the film isless distorted and more uniform in flatness.

The invention is further illustrated by the following non-limitingexamples.

EXAMPLE 1 Polyethylene terephthalate was melt extruded from a slot dieon to a rotating drum on which it was quenched to the amorphous state.The amorphous film was stretched at a temperature of about 80C with adraw ratio of about 3.021 in the longitudinal direction between a set ofslow rollers and a set of fast rollers. The film was then coated with asubbing composition, as specified below, by a reverse roll coater. Theperipheral speed of the coater roll was 40 ft/min and the speed of thefilm was 25 ft/min. The coated film was dried and then passed into astenter oven where it was stretched transversely at a draw ratio ofabout 3.0:1 while being heated at about C. The coated film was heat setin a stenter oven at a temperature of about 200C whilst being restrainedfrom shrinkage in the longitudinal and transverse directions. Thepolyethylene terephthalate film had a thickness of 7 X 10' inch and thecoat weight of the subbing coating was 4 mg/dm per side on the finishedoriented and heat set film.

The polymeric component of the subbing composition consisted of aterpolymer of, by weight, 36.8 mole percent hutadicne, 60.5 mole percentparts styrene and 2.7 mole percent itaconic acid.

This polymeric component was used to make the subhing coating having thefollowing composition. measurcd in parts by weight:

l parts Butadienc/styrcne/itaconic acid copolymer l part Gelatin 1 partAetive" anionic emulsifier available under the Trade Name Teepol 610 88parts Distilled Water.

A light sensitive layer comprising a gelatino silver halide emulsion wasapplied over the subbed film base. The material obtained was subjectedto the following tests:

1. The product was split so as to sever the polymeric film and theapplied coatings. Adhesive tape was applied along the severed edge andsharply peeled off while the film was dry. The adhesive tape testprocedure was repeated eight times. The subbing and sensi tive layersremained strongly adherent to each other and the polymeric film, with notendency to crack or chip away. 2. A wet test simulating the developing,fixing and washing processes applied to the light sensitive layer waseffected by soaking the film in the appropriate solutions in sequenceunder the temperatures and for the times typically used for theseprocesses after which the coatings were penetrated to the polymeric filmby scratching with a blunt point. The region surrounding the scratch wasabraded with a sponge but the coatings remained strongly adherent toeach other and the polymeric film. 3. The product was dried for 24 hoursat room temperature and the first test repeated. There had been nodeterioration in the adhesion of the subbing and sensitive layers toeach other and to the polymeric film.

EXAMPLES 2 to 5 The procedure described in Example l was repeated toapply different subbing coatings to the polyethylene terephthalate film.The polymeric component of the subbing composition used in each examplewas the copolymer of 36.8/60.5/ 2.7 mole percentbutadienelstyrene/itaconic acid. The Table below indicates the subbingcomposition employed (components measured in parts by weight) and theresults obtained after applying the adhesion tests specified in Example1.

was strong and un- ().2 part gelatin affected by the test I part Active"conditions. The light anionic emulsifier sensitive layer bonded 'leepol610 to the subbing composition but the adhesion was not as strong asthat in Examples 1 and 2.

l0 parts Butadienel ntyrene/ituconic acid copolymer parts gelatin part"Active" anionic emulsifier "Teepol" 610 84 parts distilled water Theadhesion between the subbing and light sensitive layers was strong andunaffected by the test conditions but the adhesion of the subbinglayerto the polymeric film was not as strong as in Examples 1. 2 and 3.

5 parts Butadiene/ styrenelitaconic acid The subbing and light sensitivelayers were copolymer strongly adherent to each other and the l partgelatin polymeric film. The

adhesion was un- 0.5 pan Active" affected by the 1 anionic emulsifierThe heat-set subbed film base prepared in Example 2 was coated by areverse roll coater with an aqueous gelatin composition having thefollowing constitution, measured in parts by weight 2 parts gelatin 0.2part formalin (40 percent by weight solution of formaldehyde) 97.8 partswater During coating the film base was transported past the roller at 25ft/min and the roller had a peripheral speed of ft/min.

The coated film base was seasoned by heating in an air oven for 3minutes at C. The seasoned gelatin coating had a coat weight of 3 mg/dm.

The test specified in Example 1 was applied to the subbed film base andit was found that a satisfactory strong adhesion existed between thepolymeric/water permeable layer and the gelatin layer which wasunaffected by the conditions of the test.

We claim:

1. A method of producing a photographic film base, which comprisescasting a flat polymeric film, molecularly orienting the cast film bystretching it in at least one direction and coating the film with asubbing composition comprising a polymeric component and a waterpermeable component selected from the group consisting of gelatin andgelatin derivatives in the range of 3.3:1 to 20:1 by weight prior to thecompletion of the molecular orientation and heat setting the orientedand coated film.

2. A method according to claim I. in which the polymeric film is apolyethylene terephthalate film.

3. A method according to claim 2, in which the cast film is biaxiallyoriented by stretching in its longitudinal and transverse directions insequence, or vice versa, and the subbing composition is applied to thefilm after stretching in the first direction and before stretching inthe second direction.

4. A method according to claim 1, in which the subbing composition isapplied as a solution and is dried before the subsequent stretchingoperation.

5. A method according to claim I, in which the subbing compositioncomprises 0.4 to 2 percent by weight of the water permeable component.

10 ing, by weight 23 parts of butadiene, 73 parts of styrene and 4 partsof itaconic acid.

9. A method according to claim 1, in which, a gelatin subbing layer isapplied over the layer comprising the polymeric component and the waterpermeable component and the film base is heated at a temperature from toC to effect bonding between the two layers.

2. A method according to claim 1, in which the polymeric film is apolyethylene terephthalate film.
 3. A method according to claim 2, inwhich the cast film is biaxially oriented by stretching in itslongitudinal and transverse directions in sequence, or vice versa, andthe subbing composition is applied to the film after stretching in thefirst direction and before stretching in the second direction.
 4. Amethod according to claim 1, in which the subbing composition is appliedas a solution and is dried before the subsequent stretching operation.5. A method according to claim 1, in which the subbing compositioncomprises 0.4 to 2 percent by weight of the water permeable component.6. A method according to claim 1, in which the subbing compositioncomprises 5.0 to 12.0 percent by weight of the polymeric component.
 7. Amethod according to claim 1, in which the polymeric component comprisesa copolymer of butadiene with one or more comonomers chosen fromacrylonitrile, styrene, methyl methacrylate methacrylic acid anditaconic acid.
 8. A method according to claim 7 in which the polymericcomponent is a butadiene terpolymer comprising, by weight 23 parts ofbutadiene, 73 parts of styrene and 4 parts of itaconic acid.
 9. A methodaccording to claim 1, in which, a gelatin subbing layer is applied overthe layer comprising the polymeric component and the water permeablecomponent and the film base is heated at a temperature from 80* to 110*Cto effect bonding between the two layers.